1. Field of the Invention
This invention relates generally to the field of controls for electronic equipment and more particularly to waterproof rotatable controls which are protected from overtorquing and contain an integral momentary contact switch.
2. Background of the Invention
As the state of the art in the electronic industry progresses, the obvious trend is towards smaller and smaller electronic devices which must reliably perform more and more functions. An excellent example of this trend is in the field of electronic calculators. While the predecessor of the modern pocket calculator literally occupied rooms devices now exist with similar computational power which will fit in a shirt pocket. These devices typically have control buttons which electronically address a number of different features per button in order to provide the user with a large number of features in a small package. This is accomplished electronically however rather than electro-mechanically.
Similar progress is taking place in the field of portable ratios and pagers. As the size of these devices diminishes, the number of control features incorporated in a single control knob must increase in order for the user to control the additional electronic features incorporated therein. Smaller portable two-way radio designs must to either decrease the size of these electro-mechanical controls to the point of being difficult to use or incorporate a number of these functions in a single control.
While the state of the art trend is towards smaller size, the need for durability and reliability in harsh artificial and natural environments is ever increasing. One of the more frequent consumer demands is for a radio which is impervious to water and rain damage. The control panel of a two-way radio or similar equipment is especially susceptible to becoming the point of entry for water and rain. The long felt need for a waterproof two-way radio is evidenced by the great commercial success of products such as the Motorola HT 440 Waterproof Portable Two-Way Radio.
Another durability and reliability problem which is frequently encountered in the field of two-way portable radios is that of damage to potentiometers caused by the user overtorquing control knobs. For electrical, size, and cost considerations, it is desirable to use physically small potentiometers and switches to control radio funtions, such as volume and squelch. These smaller potentiometers, however, are normally more fragile than larger potentiometers. Therefore, as product size decreases and the demand for reliability increases the need to protect these potentiometers from overtorquing damage is amplified.
In attempting to attain all of the above goals, severe technical difficulties are encountered when conventional design approaches are utilized. Such a conventional approach to obtaining the combined rotary function with a momentary switch might entail spring loading the control knob so the user would indirectly actuate a separate momentary switch by pressing the entire knob inward. It is known in the art to effect the combination of conventional push on/push off switches with rotary knobs in this manner. However, water sealing such an assembly without sacrifice in reliability becomes next to impossible. Such a design would probably require the control's shaft to slide longitudinally through an O-ring seal. It is well known that this type of movement produces shear stresses in the O-ring and induces failure of the seal after very few operations. In addition, the force required to operate such a control and the spring pressure required to return such a control to its original position would be excessively high and would translate into greater expense and highly inefficient utilization of space due to thicker housing walls, more support structures, etc.
Since it is also desirable to electrically insulate the control to prevent corrosion, and to incorporate overtorquing protection, the above approach is totally unsatisfactory.